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Lennox slp98v help please

Hello all at HVAC talk. I had a SLP98v Lennox gas furnace installed in place of a 1991 80+ about 6 weeks ago in December. The first thee weeks it was great. It was quite and the house has never been more comfortable. The gas bill came and again could have been happier.

Then the honeymoon came to a screeching halt. Condensate problems...... The inducer fan sounds like a flushing toilet at first then in second and third stage is sound like a turbo spooling up. Motor gets very hot. I'm now on the installers thrid attempt in fixing the issue. First was extending the trap. Second was replacing the inducer motor and fan assembley. They also put the proper slight lean to the left where the trap is on the furnace. When he took the old fan assembly out it was full of condensate.....not good. That fix worked for about three hours before you start to hear the water bouncing around when the inducer starts up.

Some basic info. I have about thirty feet of instake and exhaust. The first 5-6' is 2 inch then stepped up to three until it terminates. They checked the pitch and it seemed alright. As I mentioned the trap is on the left side. The furnace was installed with a slight lean back and to the right which was 100% wrong. This has been corrected but we are still having issues.

The next fix is the installer wants to put a T in the exhaust at the 2 to 3" transition, drill out and install a drain with a looped trap. Not sure if I'm crazy about that. Not sure if the State of Michigan inspector or Lennox would either.

It is draining some condensate into the pump but obviously not all.

Its getting a little frustrating to pay what I did for one of the quietest furnaces on the market and it sounds like a cross between a flushing toilet and deisel engine.

Any ideas for a fix or Lennox updates for the problem? How about my installer installing a drain in the exhaust line? Thanks for anything you can bring to the table.

With the condensate trap on the left hand side the unit needs to be raised 1/2 inch in the rear. That is per Lennox. I've had mine now since 12/21/2011 and not had any issues. Verify that your condensate drain is separate from all other drains and isn't plugged. My furnace produces ALOT of condensate but have never had any issue with it draining properly.

I agree with SJ's post. Make sure the drain line isn't tied directly into the evaporator's drain port. If the drains are together, there must be a filled trap in the evaporator side, to resist or block the positive air pressure. If it is tied directly together, or the evap trap is dry, you could be getting the positive air static pressure backing up the furnace's drain trap. A vent immediately after the evap trap with help relieve the static pressure. Also, if you have an extension on the drain line outside the home, it could be frozen causing a drain back up.

Lennox prefer's the trap on the right side, not the left. Multiple issues. They are documented and on davenet.com. No matter where the trap is, the furnace should be leaning forward about 1/4 of an inch.

I agree with SJ's post. Make sure the drain line isn't tied directly into the evaporator's drain port. If the drains are together, there must be a filled trap in the evaporator side, to resist or block the positive air pressure. If it is tied directly together, or the evap trap is dry, you could be getting the positive air static pressure backing up the furnace's drain trap. A vent immediately after the evap trap with help relieve the static pressure. Also, if you have an extension on the drain line outside the home, it could be frozen causing a drain back up.

They did put a vent extending upward on the condensate trap. That unfortunately didn't work. It actually was worse. Probably a coincidence. They also shimmed the furnace between a 1/4" and 1/2" forward towards the trap on the left. As far as being tied together they only meet at the condensate pump. Would that still be an issue? There are 4 inlets on the pump one for the condensate, one for the evaporator and one is the humidifier drain. I'll try to get pics tonight so you can see what has all been done

As Greg says, Lennox had an issue with the packaging of the furnace drain trap. It was in a sealed bag with other items including small wire nuts that could get jammed inside the trap during shipping. If the installer did not know of the issue, he could have easily installed the trap with a wire nut trapped inside clogging up the drain.

As promised here are the pics. I was mistaken when I said the condensate trap line and evaporator drain line were seperated until the go into the condensate pump. As you can see in the pics they are connected via a T before the pump. They did vent the trap as it exits the left side. Is this acceptable or do they still need to seperate it? Might this be the cause of my issues?

Also in the 4th pic you can see the intake and exhaust. Exhaust is on the left. The installer wants to add a drain as it reduces down, loop the line then drain back into the condensate pump....Any thoughts on that practice? Would that pass my Michigan inspection? Is a potential Carbon Monoxide hazard.

I will have then check for anything loose that could be plugging the trap like wire nuts. They will be out again on Tuesday.

Last question. They installer a White-Rodgers 80 Seriesฎ Programmable Thermostat. Is this limiting the full functionality of the furnace. Not sure if its multi-stage or not. Would I be better off with a Comfort Sense 7000 in terms of maximizing the furnaces potential. That is.....assuming I can get past the current issues with condensate build up.

You all have been a great help and I have lots of things to bring up with the tech to check on....because he seems befuddled.

On page 25 of the installation manual it states "CAUTION! A separate drain line must be run to the drain from thecondensate trap. DO NOT connect the condensate trap drain into the drain line from the evaporator coil." I would also verify the slope on the line exiting your trap.

What size is this furnace? Even on the 90k up to 24' of 2" pipe is allowed with 10 elbows. Why did they go up to 3"? (See chart on pg 16 of install manual).

As far as thermostat, unless you have a non-communicating heat pump the best thermostat to use with the system is the iComfort.

Definitely check for the wire nut or anything else that may be in the trap.

Last edited by SJProwler; 01-29-2011 at 10:33 AM.
Reason: dept of redundancy dept.